In the current increasingly competitive economic environment the steelmaker must provide a product which is capable of satisfactory usage in more than one application to remain competitive in the marketplace. However, this economic dictate poses substantial challenges to the skill of the steelmaker since the operating conditions in two applications are often different and consequently the required physical and chemical characteristics are dissimilar or even in conflict.
If the steel is to be used as a mold, such as a plastic injection mold where the tool's ability to take and hold a smooth surface during long production runs is important, polishability along with high wear resistance, high hardenability, and easy machineability are key requirements. However, high strength and ductility are not as critical as the aforementioned attributes and hence the steelmaker can favor enhancement of the above mentioned key operating requirements over such attributes as high strength and ductility.
If a steel is to be used as a closed die forging tool, for example, high strength, high wear resistance, high hardenability and easy machining are essential. Fatigue resistance is not an especially critical characteristic in closed die forging since a typical die block may only be subjected to, for example, 5,000-10,000 cycles per sinking during its useful life expectancy of, for example, six or eight resinks. As a consequence the steelmaker whose product is intended to be used in closed die forging can favor enhancement of the required operating characteristics of this application such as wear resistance, impact resistance and through hardenability, over ductility and polishability, as by using alloys which contribute to the required characteristics but which do not significantly enhance ductility, and thus fatigue resistance or polishability.
If the steelmaker wishes to apply the same steel to machine part applications, such requirements as high strength, high wear resistance, high through hardness and easy machining are still important, but, in addition, ductility, and consequently fatigue resistance, must be increased since machine parts, such as gear teeth, run millions of cycles. Resistance to fracture is, generally, of lesser importance in machine parts since such parts generally are not subjected to sudden, heavy shock loads of the type encountered in closed die forging and hence the steelmaker, theoretically, can conserve on elements which contribute to fracture resistance. By the same token, the ability to take and hold a high polish is not an essential characteristic.
Thus, though high hardness, high wear resistance and through hardening are required in all applications, and said characteristics along with high strength are essential in both closed die forging applications and machine parts, polishability, fatigue resistance and fracture resistance requirements differ from environment to environment, and thus the steelmaker is faced with the task of providing a single steel which is usable in distinctly different operating environments without loading the steel with alloys which would cause the cost of the steel to the user to be so high as to be uneconomical.